docs: def get_tectonic_regionalisation(self, regionalisation, region_type=None):
          '''
          Defines the tectonic region and updates the shear modulus,
          magnitude scaling relation and displacement to length ratio using
          the regional values, if not previously defined for the fault
  
          :param regionalistion:
              Instance of the :class:
              openquake.hmtk.faults.tectonic_regionalisaion.TectonicRegionalisation
          :param str region_type:
              Name of the region type - if not in regionalisation an error will
              be raised
          '''
          if region_type:
              self.trt = region_type
          if not self.trt in regionalisation.key_list:
              raise ValueError('Tectonic region classification missing or '
                               'not defined in regionalisation')
  
          for iloc, key_val in enumerate(regionalisation.key_list):
              if self.trt in key_val:
                  self.regionalisation = regionalisation.regionalisation[iloc]
  
                  # Update undefined shear modulus from tectonic regionalisation
                  if not self.shear_modulus:
                      self.shear_modulus = self.regionalisation.shear_modulus
                  # Update undefined scaling relation from tectonic
                  # regionalisation
                  if not self.msr:
                      self.msr = self.regionalisation.scaling_rel
                  # Update undefined displacement to length ratio from tectonic
                  # regionalisation
                  if not self.disp_length_ratio:
                      self.disp_length_ratio = \
                          self.regionalisation.disp_length_ratio
                  break
          return